1. Field of the Invention
The present invention relates to a compound optical unit as a combination light receiving/emitting optical element suitably used in an optical device, such as an optical pickup, which applies light onto an optical disk and receives returned light from the optical disk in order to perform writing or reading of information on the optical disk.
2. Description of the Related Art
As an example of compound optical units, a combination light receiving/emitting optical element has been proposed and used which applies laser beam onto an optical disk or which receives laser beam from the optical disk in order to perform recording or reproduction of information on the optical disk.
To write information on an optical disk, such as a CD (compact disk), a CD-R (write-once compact disk), or a DVD (xe2x80x9cdigital versatile diskxe2x80x9d or xe2x80x9cdigital video diskxe2x80x9d), or to read information on an information-recording surface of the optical disk, an optical pickup is used, and an optical unit is mounted on the optical pickup.
When various types of optical components are mounted on the optical pickup, positions or angles of the optical components with respect to the optical pickup are adjusted so as to optimally perform writing or reading of information on the-optical disk. In this case, in an optical unit having a combination of a light receiving section and a light emitting section, the relationship between light receiving position and a light emitting position is not changed even by the adjustment. Therefore, wide allowable ranges of the positions and the angles of the optical components can be ensured, and the positions and the angles can be easily adjusted. Such an optical unit has been widely used. In order to reduce the size of the optical pickup, an optical unit has been developed of reduced size.
In recent years, DVD apparatuses for writing/reading information on a DVD, which is an optical disk having a higher recording density than a CD, have been commercialized, and reduction in cost of the DVD apparatuses is essential in order for the DVD apparatuses to become more popular. Accordingly, a reduction in cost of an optical unit used in an optical pickup to be mounted on the DVD apparatuses has been demanded.
In addition, compatibility with CDs (including CD-Rs) has been demanded for the DVD apparatuses. Therefore, the DVD apparatuses should include a laser light source (with a wavelength of 650 nm) for a DVD, and a laser light source (with a wavelength of 780 nm) for writing and reading information on the CD-R which cannot be read by a laser light source with a wavelength of 650 nm.
FIG. 5 is a plan view showing an optical pickup 20 having conventional optical units 4 and 8 mounted thereon. The optical pickup 20 is primarily composed of the optical unit 4 for a DVD (high-density optical disk) 17, the optical unit 8 for a CD (low-density optical disk) 18, a beam splitter 10 for guiding laser beams of various wavelengths, emitted from the optical units 4 and 8, to the same optical axis, a wavelength filter 15 serving as a diaphragm for restricting the diameter of the laser beam in accordance with the wavelength of the laser beam, an objective lens 16, and a carriage 21 for disposing the above components at predetermined positions so as to be able to read information from both the DVD 17 and CD 18.
The above components will now be described in detail.
The optical unit 4 is composed of a light source 2, which is a laser diode chip for emitting laser beam of a wavelength of 650 nm for the DVD 17; a light-receiving element 3 consisting of a photo-diode serving as a light receiving member for receiving laser beam reflected by the DVD 17; a base plate 4a having the light source 2 and the light-receiving element 3, a side wall 4b fixed to the base plate 4a contains the light source 2 and the light-receiving element 3; an emergent section 4d that is a window in the side wall 4b; and a highly transmissive optical member 5, such as glass, bonded to cover the emergent section 4d. The light source 2 is fixed on the base plate 4a so as to oppose the optical member 5, and the light-receiving element 3 is formed on the surface of the base plate 4a in close proximity to the light source 2. In addition, laser beam (returned light) emitted from the light source 2 and reflected by the DVD 17 is diffracted by a diffraction grating 5a formed on the optical member 5 so as to be guided to a predetermined position of the light-receiving element 3. Since a sufficiently large diffraction angle of the returned light diffracted by the diffraction grating 5a is not obtained because narrowing of the pitch of the diffraction grating 5a is limited (the narrower the pitch of the grating, the larger the diffraction angle obtained), the light-receiving element 3 is formed in close proximity to the light source 2. The optical member 5 is fixed to the emergent section 4d after the position thereof has been adjusted so that the light diffracted by the diffraction grating 5a is guided to a predetermined position of the light-receiving element 3 by a predetermined reference optical system.
The optical unit 8 is composed of a light source 6 that is a laser diode chip for emitting laser light of a wavelength of 780 nm for the CD 18; a light-receiving element 7 consisting of a photo-diode for receiving laser beam reflected by the CD 18; a base plate 8a having the light source 6 and the light-receiving element 7, a side wall 8b fixed to the base plate 8a to contain the light source 6 and the light-receiving element 7; an emergent section 8d that is a window in the side wall 8b; and a highly transmissive optical member 9, such as glass, bonded to cover the emergent section 8d. The light source 6 is fixed on the base plate 8a so as to oppose the optical member 9, and the light-receiving element 7 is formed on the surface of the base plate 8a in close proximity to the light source 6. Returned light emitted from the light source 6 and reflected by the CD 18 is diffracted by a diffraction grating 9a formed on the optical member 9 so as to be guided to a predetermined position of the light-receiving element 7.
The light-receiving element 7 is formed in close proximity to the light source 6 for the same reason as for the optical unit 4. In order to effect tracking control by a three-beam method, the optical member 9 is provided with a beam formation section 9b. The optical member 9 is fixed to the emergent section 8d after the position thereof has been adjusted so that the light diffracted by the diffraction grating 9a is guided to a predetermined position of the light-receiving element 7 by a predetermined reference optical system.
The beam splitter 10 guides both laser beams from the light source 2 and the light source 6 to the DVD 17 (CD 18). The beam splitter 10 is shaped like a rectangular parallelepiped in which two prisms are bonded to each other, and a bonding surface is coated with an optical film (dichroic film) having a wavelength selecting function. The dichroic film is formed so as to transmit the laser beam for the CD 18 and to reflect the laser beam for the DVD 17.
The wavelength filter 15 is formed so as to transmit the laser beam emitted from the light source 2, and to reflect or absorb the laser light emitted from the light source 6, thereby restricting diameters of laser beams emitted from the light source 2 and the light source 6. Therefore, when spots of laser beams emitted from the light sources 2 and 6 and condensed by the objective lens 16 are applied onto the DVD 17 and CD 18, respectively, aberration is reduced.
Dispositions of the optical units 4 and 8, and reading of information of the DVD 17 and CD 18 will now be described in detail.
The optical unit 4 and the optical unit 8 are disposed to form an angle of about 90xc2x0 starting from the beam splitter 10. The optical unit 8 is disposed in a direction nearly parallel to an optical axis of light travelling from the wavelength filter 15 to the objective lens 6, and the optical unit 4 is disposed in a direction nearly perpendicular to an optical axis travelling from the wavelength filter 15 to the objective lens 16.
In such a configuration, when reading information from the DVD 17, the laser light emitted from the light source 2 at a wavelength of 650 nm passes through the emergent section 4d and the diffraction grating 5a to enter the beam splitter 10. The laser beam incident on the beam splitter 10 is reflected and is emitted therefrom while the optical axis thereof is bent about 90xc2x0, and enters the wavelength filter 15 provided adjacent to the beam splitter 10. The laser beam for the DVD 17 from the light source 2 is transmitted by the wavelength filter 15 with almost no restriction of the diameter thereof. The laser beam transmitted by the wavelength filter 15 enters the objective lens 16, and is then focused on an information-recording surface of the DVD 17 by a focusing action of the objective lens 16.
Thereafter, the laser beam reflected by the DVD 17 is transmitted by the objective lens 16 and the wavelength film 15 again, is reflected by the beam splitter 10 while the optical axis thereof is bent toward the optical unit 4, and enters the diffraction grating 5a. The laser beam is diffracted by the diffraction grating 5a to enter the light receiving section formed on the light-receiving element 3. In this case, the laser beam incident on the light receiving section is subjected to photoelectric conversion, whereby reading signals, obtained by converting current outputs according to the signals on the information-recording surface of the DVD 17 into voltage signals, are formed and output from external terminals 4c of the optical unit 4. In addition, a part of a laser beam incident on the light receiving section is used for focusing control and tracking control.
On the other hand, when reading the information from the CD 18, the laser beam emitted from the light source 6 at an oscillation wavelength of 780 nm passes through the emergent section 8d, the beam formation section 9b, and the diffraction grating 9a. In this case, the laser beam consisting of three beams formed by the beam formation section 9b enters the beam splitter 10. The laser beam incident on the beam splitter 10 is transmitted by the beam splitter 10, is emitted unchanged from the beam splitter 10, and enters the wavelength filter 15 formed adjacent to the beam splitter 10. The laser beam for the CD 18 from the light source 6 is reflected by zones formed on the outer peripheral portion of the wavelength filter 15 and is transmitted by a portion where the zones are not formed, whereby the wavelength filter 15 functions like a diaphragm for the laser beam for the CD 18 and restricts the diameter of the laser beam entering the objective lens 16. The laser beam transmitted by the wavelength film 15 enters the objective lens 16. Then, the laser beam is focused on an information-recording surface of the CD 18 by a focusing action of the objective lens 16.
Thereafter, the laser beam reflected by the CD 18 is transmitted by the objective lens 16 and the wavelength film 15 again, and is transmitted by the beam splitter 10 to enter the diffraction grating 9a. The laser beam is diffracted by the diffraction grating 9a to enter the light receiving section formed on the light-receiving element 7 without being caught by the beam formation section 9b. In this case, the laser beam incident on the light receiving section is subjected to photoelectric conversion, whereby reading signals, obtained by converting current outputs according to the signals on the information-bearding surface of the CD 18 into voltage signals, are formed and output from external terminals 8c of the optical unit 8. In addition, a part of the laser beam incident on the light receiving section is used for focusing control and tracking control by a three-beam method.
As described above, in the conventional optical unit 4 (8) shown in FIG. 5, the minute light source 2 (6) and light-receiving element 3 (7) are disposed side by side in close proximity to each other on the base plate 4a (8a), the side wall 4b (8b) is fixed to the base plate 4a (8a) to contain the light source 2 (6) and the light-receiving element 3 (7), and the minute optical member 5 (9) is bonded to the emergent section 4d (8d) of the side wall 4b (8b), thereby reducing the size of the optical unit 4 (8). Therefore, the conventional optical unit 4 (8) is suitable for reduction in size of an optical pickup.
However, while a small optical pickup is necessary for use in a portable device, such as a notebook personal computer, the need is increasing for an optical pickup which can reduce cost rather than size.
In the conventional optical unit, a minute laser diode chip is used as the light source 2 (6), and a minute photodiode formed on the surface of the base plate 4a (8a) by a process similar to a semiconductor process is used as the light-receiving element 3 (7), and the minute optical member 5 (9) is used. Therefore, it is difficult to handle these components, and a delicate operation for fixing or forming the components on the base plate 4a (8a) is required, resulting in increased process cost and increased cost of the optical unit.
In addition, in order to guide returned light from the optical disk to the light-receiving element 3 (7), the conventional optical unit 4 (8) includes the optical member 5 (9) having the diffraction grating 5a (9a) which can be formed at low cost with a simple structure. The cost of the optical unit 4 may be reduced by using the diffraction grating 5a (9a) and by merely replacing the light source 2 (6) and the light-receiving element 3 (7) with a semiconductor laser and a light-receiving element consisting of discrete components that are available at low cost and are easy to handle. This method, however, cannot be adopted because the space between a light emitting point of the semiconductor laser and a light receiving position of the light-receiving element cannot be reduced. Furthermore, diffracted returned light cannot be received by the light-receiving element of the diffraction grating 5a (9a), which cannot yield a sufficiently large diffraction angle as described above.
On the other hand, if the space between the optical member 5 (9) and the semiconductor laser and the light-receiving element consisting of discrete components are increased sufficiently, an optical unit can be formed even with the configuration of the conventional optical unit 4 (8). However, the size of the optical unit is considerably increased and an optical unit of practical size cannot be formed.
In addition, when the optical unit is incorporated into the optical pickup serving as an optical device using light sources for emitting light of two different wavelengths, two optical units 4 and 8 corresponding to the two wavelengths should be used, resulting in an increased number of components and a complicated structure of the optical pickup.
Accordingly, it is an object of the present invention to provide a compound optical unit which is able to reduce the cost of the unit, which is able to correspond to an optical device using a plurality of light sources for emitting light of different wavelengths even in the case of one compound optical unit, and which can also be applied to the optical pickup.
According to an aspect of the present invention, there is provided a compound optical unit including a housing mounted on an optical device. A light emitting mechanism, a light receiving member, and a composite optical member are integrally fixed to the housing. The light emitting member includes a light-emitting element and a first package containing the light-emitting element. The light-receiving member includes a light-receiving element and a second package containing the light-receiving element. The housing includes an entering/emitting opening to emit light emitted from the light emitting member and to admit returned light from the optical device. The composite optical member is disposed among the entering/emitting opening, the light emitting member, and the light receiving member.
In the compound optical unit, the composite optical member may preferably include an incidence surface to admit light emitted from the light emitting member, a first emission surface to emit the light from the light emitting member, a diffracting mechanism provided on the first emission surface to diffract the returned light, a reflecting surface to reflect light diffracted by the diffracting device, and a second emission surface to emit light reflected by the reflecting surface toward the light receiving member.
In addition, the diffracting mechanism may preferably include a diffraction grating having a rugged part directly formed on the emission surface.
Furthermore, the composite optical member including the diffraction grating may preferably be made of resin, and may be integrally formed by molding.
Furthermore, in the compound optical unit, a plurality of light emitting members each having the light-emitting elements of different wavelengths may preferably be provided, and a multiplexor to multiplex light emitted from each of the light emitting members in along a parallel optical path may preferably be provided on the housing.
The multiplexor may be combined with the composite optical member.
In addition, the multiplexor may comprise a prism having an optical film that transmits or reflects the light emitted from each of the light emitting members, and the prism may be fixed to the composite optical member with the optical film plane-joined to a part of the composite optical member.
In the compound optical unit, the light receiving member may have a plurality of the light-receiving elements of different wavelengths.
In addition, the optical device may comprise an optical pickup which is equipped with an objective lens and which performs writing or reading of information on an optical disk, and light emitted from the light emitting member may be applied to the optical disk through the objective lens, and returned light from the optical disk may be received by the light receiving member.
Furthermore, the composite optical member may include an incidence surface to admit light from the light emitting member, a first emission surface to emit the light from the light emitting member, a diffracting mechanism provided on the first emission surface to diffract the returned light, a reflecting surface to reflect light diffracted by the diffracting mechanism, and a second emission surface to emit light reflected by the reflecting surface toward the light receiving member.
In another embodiment, the compound optical unit comprises an optical device mounted on a housing. A composite optical member is integrally fixed to the housing and disposed between a light emitting element and a light receiving element. Light from the light emitting element is transmitted through the composite optical member towards the optical device and light returning from the optical member is directed through the composite optical member towards the light receiving element.
The composite optical member may comprise a diffracting mechanism provided on the composite optical member to diffract the light returning from the optical device and a reflecting surface provided on the composite optical member to reflect light diffracted by the diffracting mechanism towards the light receiving element. The reflecting surface is inclined towards the light receiving element.
The diffracting mechanism may comprise a diffraction grating including a rugged part directly formed on a surface of the composite optical member. The composite optical member and the diffraction grating may be integrally formed.
The composite optical member may include a plurality of light-emitting elements of different wavelengths and a multiplexor to multiplex light emitted from the light emitting elements along an optical path provided in the housing. The multiplexor may be fixed to the composite optical member. The multiplexor, in addition, may include a prism having an optical film to transmit or reflect light emitted from each light emitting element. The prism may be fixed to the composite optical member with the optical film plane-joined to a surface of the composite optical member. The composite optical member may comprise a rectangular parallelepiped section.
The compound optical unit may further comprise a plurality of light receiving elements of different wavelengths contained within a light receiving member.
The optical device may include an optical pickup equipped with an objective lens and performing reading or writing of information on an optical disk, for which the light emitted from the light emitting element is applied to the optical disk through the objective lens and the light returning from the optical disk is received by the light receiving element. The optical device may include a DVD player or a read/write recordable player. The light emitting element and light receiving element may be discrete electronic components.